1. Field of the Invention
This invention relates to an LED messaging sign panel. More particularly, it relates to a system which permits multiple modular LED messaging sign panels to be attached to create a larger panel display system yet retaining a means for addressing the individual LED sign panels within the display system.
2. Description of Prior Art
LED (light emitting diode) sign panels are known in the prior art. Typically, a display matrix of LEDs is arranged in a row-column array. For instance, in U.S. Pat. No. 4,445,132 to Ichikawa et al., 8.times.8, 12.times.12 and 16.times.16 arrays are shown wherein the first numeral represents the number of rows of LEDs and the second numeral represents the number of columns of LEDs. These rows and columns of LEDs formed a flat panel LED display. Although flat panel displays can be made in order to utilize different light sources (i.e., electroluminescence, plasma, fluorescent tube or incandescent bulbs), LED flat panel displays have become one of the most popular formats to use for displaying information and messages. Reasons for LED popularity include smaller operation voltages and reduced current requirements as compared to other types of light sources.
Unfortunately, most LED display designers discovered that it was difficult to manufacture very large LED display panels. Many of the benefits conferred from the use of LED technology did not outweigh the problems inherent with the construction of large display panels. Therefore, it was proposed that modular panels of smaller arrays be utilized, attachable to one another, to form a single larger display panel.
U.S. Pat. No. 5,450,301 to Waltz et al. proposes the use of modular panels of smaller arrays to form a larger LED display panel. Unfortunately, there is no teaching for individual operator control of each module in the field. The individual modules are merely elements of the larger display. Waltz et al. does not permit an operator to address or control each module individually. Further, such a configuration requires multiple wire connections between each module. This may present problems in troubleshooting the individual panels. Further, there is no teaching for controlling the Waltz et al. device by a computer. Computer control of LED display panels is recognized as a useful feature in the display of messages and other information.
Other designers, recognizing the benefits that computer controlled LED displays would provide, began developing systems which permit computer control. U.S. Pat. No. 4,887,074 to Simon et al. discloses a computer-controlled LED display system which utilizes a multitude of parallel port outputs of a computer to shift data through a multitude of shift registers, including parallel-in-parallel-out (PIPO), parallel-in-serial-out (PISO) and serial-in-parallel-out (SEPO) registers all in an effort to drive a single LED array. Although such a system permits the operator to utilize the benefits of computer to display a graphic file on the display panel, the shifting of data through a plurality of shift registers in the vertical and horizontal directions is inefficient. Such a system is analogous to a multiplexing system which operates by scanning each row of LEDs in the array in a discernable time frame thereby giving the illusion that the picture is being displayed across the entire panel at the same time--much like the technique used in conventional TV picture tube displays. Multiplexing systems have inherent disadvantages; one such disadvantage is the slow refresh display rates due to the required time to scan the entire display panel. None of the prior art systems permit an entire display panel to show a graphic along all of its vertical and horizontal arrays simultaneously while loading the next frame directly behind it within an entire digital domain.
Another inherent problem in the prior art systems relates to brightness control and correction. Because of the large size of many display systems, a drop in the overall brightness of the display panel and varying brightness from module to module within the display panel system can be evident due to the increase in load requirements upon the power supply of a large display system. Brightness control circuits have been implemented along with the circuitry of the LED driving circuits to control and correct brightness. Such can been seen in U.S. Pat. No. 5,451,979 to Levac whereby the expected load is determined during a refresh scan that is about to produce the next image. The number of LEDs to be energized is counted and compared to a duty cycle index table stored in memory. The display refresh duty cycle is then adjusted depending on an expected increase or decrease in the power supply load requirement. Although such a routine permits an unregulated power supply output to be maintained within preselected limits thereby increasing the output to handle peak loads and decreasing the output to handle low loads, such a system does not ensure that a decrease in each light across the entire display panel will not occur. In fact, the Levac system compromises overall panel brightness in favor of uniform brightness from LED to LED.
Due to all of the deficiencies in the prior art, an improved LED display panel system is needed.